Method for microstructuring by means of locally selective sublimation

ABSTRACT

A method for microstructuring by means of locally selective sublimation is disclosed, whereby patterns or images of organic electroluminescent components are produced by application of low molecular weight emission material, provided on a support, to those points of substrate corresponding to the pattern or image for production, by means of sublimation. According to the invention, the method is carried out by firstly completely coating a film support made from temperature-resistant material with the emission material. The coated support and the substrate are then placed adjacent and parallel to each other in a vacuum chamber. The side of the support coated with the emission material faces the substrate. The support is subsequently locally heated for a short period of time on the non-coated side thereof in those positions corresponding to the pattern or image for generation, to a temperature adequate for the sublimation of the emission material.

The invention concerns a method for microstructuring by means of locallyselective sublimation, whereby patterns or images of organicelectroluminescent components are applied by means of sublimation to alow molecular emissions material provided on a support, to those pointsof a substrate which correspond to the pattern or image to be produced(US-Z “Applied Physics Letters” vol. 74, no. 13, Mar. 29, 1999, pages1913 to 1915).

Such a method is used to advantage for the production of displays.Beyond that it can also be used for example to produce laser structuresor modular structures based on organic materials. A display is composedof individual picture points “pixels” which can be individuallycontrolled electrically, and are used to display any desired patterns orimages. Displays are used for example as a visual interface between manand machine. They can also be computer monitors or mobile telephones.Since the method for microstructuring is essentially performed in thesame way for all indicated applications, the following indications referto the production of displays and represent all other applicationpossibilities.

The displays can be single color or multicolor as well. So-called RGBdisplays comprise the three colors red, green and blue. When an electricvoltage is applied to a display, the electroluminescent componentscontained therein begin to give off light.

For example an “Organic Light Emitting Diode” is an organicelectroluminescent component, hereafter simply called “OLED”. OLEDs havegreat advantages for the production of patterns on flat supports,so-called displays, namely due because of relatively simple constructionand because noncrystalline materials are used. These advantages applyparticularly to other types of displays, such as liquid crystal displaysor cathode-ray tubes. OLEDs can be made of polymer (PLED) or oflow-molecular (SMOLED) organic materials.

The methods for producing OLEDs from PLEDs and SMOLEDs are well known.Materials that can be used for PLEDs are applicable for example indissolved form next to each other by means of printing techniques(inkjet, silk screen) in an additive process. This is not possible forSMOLEDs. These are produced with known techniques by sublimating therespective materials from evaporative sources in a high vacuum. In thatcase the sublimated material is precipitated during the gas phase as athin film over the entire surface of a substrate. The formation of afilm over the entire surface by means of this technique is usually onlypossible at great expense, since the low-molecular materials being usedcan be easily damaged. An interruption of the vacuum to bring about thisformation also reduces the quality of the SMOLEDs drastically. Thisapplies even more to full-color displays, where each picture pointrequires the separation of three closely adjacent pixels with theemission colors of red, green and blue. In addition it must be ensuredthat the local application of the different pixels or organic layers canbe done without damaging any of the existing layers.

To that end the known method according to the above mentioned US-Z“Applied Physics Letters” uses masks called “shadow masks”. In that casethe display substrate is covered with a mask before the organic materialis sublimated. The mask is placed at a small distance from the front ofthe substrate. It only contains openings where a pixel of the organicmaterial is to be produced. Materials for different colors can also beselectively applied by shifting the mask with respect to the substratethe distance of one pixel between sublimation steps. Because of thenecessary high dissolution of the matrix structure, any mask used forthis method must have a very fine grid. The mask furthermore must have aslender material thickness. Both requirements only provide a lowmechanical stability to the mask. This makes the exact positioning andaffixing of the mechanically unstable mask difficult, particularly forlarger displays. The constant precipitation of sublimated material onthe mask also causes its openings to become rapidly clogged, makingfrequent mask cleaning or mask changing necessary.

The object of the invention is to simplify the above described method.This object is achieved by the invention in that:

-   -   first a film support made from a temperature resistant material        is completely coated with the emissions material,    -   then the coated support and the substrate are placed closely        adjacent and parallel to each other in a vacuum chamber, where        the side of the support that is coated with the emissions        material faces the substrate, and    -   the local positions on the uncoated side of the support which        correspond to the pattern or image to be produced are then        briefly heated to a temperature that is sufficient for the        sublimation of the emissions material.

With this method a film, hereafter called a “film support”, made of atemperature resistant material such as polyimide for example, is firstcompletely coated with an emissions material. To selectively transferthe emissions material to the substrate provided for storing a patternor image, hereafter called a “display substrate”, it is then placed in avacuum chamber at a small distance from the film support so that theside coated with the emissions material faces the display substrate. Bybriefly and locally heating the uncoated side of the film support theemissions material is sublimated and deposited on the display substrate.Because of the small distance between the film support and the displaysubstrate, in this case the expansion of the area that is coated withthe material corresponds very accurately to the expansion of the heatedarea.

The film support can be very quickly and cost-effectively coated withthe organic material to be sublimated when simple methods are used. Forexample if layers of different organic materials are applied tosuccessive areas of the film support, simply advancing the film supportbetween two sublimation steps allows stacks of organic layers, oradjacent pixels with the appropriate control of the heating elements, tobe produced with different emissions colors in an uninterrupted process.However separate film supports can also be used if they are coated withthe different organic materials and are successively placed intoposition.

The thin organic layer of emissions materials and the film supportcarrying it have a low heat capacity. The local heating including thefull transfer of the emissions material to the display substrate canthen happen within fractions of seconds. Since the local heating takesplace in small delimited areas, this method allows to achieve a highlateral dissolution. The local heating can be accomplished withfine-structured electrical heating elements, or with laser radiation inconjunction with the corresponding optics. As already mentioned, in bothcases the transfer of the structure can take place simultaneously forall pixels, and consecutively for individual columns or pixels as well.No mechanical moving parts are needed in the vacuum chamber whenelectrical heating elements or any optical-radiational heating are used.

To adjust the emissions color the film support can also be coated withtwo successive low-molecular layers, a material A on one side and amaterial B on the other. The material A is called the host material andmaterial B is the guest material. The two materials are not intermixedon the film support. A mixed layers is created on the display substrateafter the sublimation step, where the material A is doped with thematerial B. The material B produces a light emission. The material Bdetermines the respective emissions color.

The method according to the invention is explained as an embodiment bymeans of the drawings, wherein:

FIG. 1 schematically shows a process of the method according to theinvention.

FIG. 2 shows the film support and display substrate arrangement duringthe course of the process.

A film support 1 made of a temperature resistant material, polyimide forexample, is moved to an arrangement 2 where an emissions material isdeposited on one of its sides by means of sublimation. The other side ofthe film support 1 remains uncoated. A thin adhesive layer of theemissions material completely covers the corresponding side of the filmsupport 1. The film support 1 can have a thickness of about 100 ìm forexample. It can also be made of a different temperature resistantmaterial than polyimide. The layer of emissions material can be about 10nm-1 ìm thick. The arrangement 2 can be a high vacuum chamber with theusual sublimation sources. But it can also be arranged as a dipping,spraying or printing device. The emissions material is a low-molecularorganic material, such as for example aluminum-tris (8-hydroxyquinoline)(briefly: Alq₃, emissions color green) or with4-dicyanomethylene)-2-methyl-6-(p-dimethylamine-styrene)-4H-pyran(briefly: DCM) doped Alq₃ (which then becomes DCM: Alq₃, emissions colorred), or 2,2′,7,7′-tetrakis (2,2′-diphenylvinyl)spiro-9,9′-byfluorine(briefly: Spiro-DPV-Bi, emissions color blue).

The film support 1 coated with the emissions material and a displaysubstrate 3 are placed in a vacuum chamber 4. There the film support 1and the display substrate 3 are positioned closely adjacent and parallelto each other as shown in FIG. 2. Their distance from each other isbetween about 5 ìm and 200 ìm in accordance with the scale of thedesired dissolution. A preferred method uses a distance of 50 ìm forexample.

Before the emissions material is applied to predetermined areas of thedisplay substrate 3, the back side of film support 1 is briefly andlocally heated as shown by the arrows 5. The emissions material is thendeposited on the display substrate 3 by means of sublimation.Temperatures between 100° C. and 500° C. can be used. The local heatingcan be achieved with fine-structured electrical heating elements, orwith laser radiation or intense lamp radiation, for example with halogenlamps, in conjunction with the corresponding optics. In both cases thetransfer of the structure can take place simultaneously for all pixelsand consecutively for individual columns or pixels as well. Theexpansion of the area that is thereby coated with the emissions materialcorresponds very accurately to the expansion of the heated area becauseof the small distance between the film support 1 and the displaysubstrate 3.

A film support 1 coated with the desired emissions material is used toproduce single color displays. Full color RGB displays require the useof three film supports 1, each of which is coated with an emissionsmaterial. The film supports 1 are then successively placed in thecorrect position with respect to the display substrate 3 and heatedlocally. However it is also possible to coat adjacent areas of a filmsupport 1 with different emissions materials. The film support 1 thenonly needs to be shifted accordingly during the sublimation steps.

To adjust the emissions color, the film support 1 can also be coatedwith low-molecular materials in two consecutive steps so that thematerials are not intermixed. These are for example a host material Aand a guest material B which differs from the former. The sublimationstep produces a mixed layer on the display substrate 3 where the hostmaterial A is doped with the guest material B. The guest material Bproduces a light emission and determines the emissions color.

Beyond that the method can also be used for low-molecular materialswhich improve the transport or the injection of electrical chargecarriers. A suitable material is for example 4,4′,4″-tris(N-(1-naphthylamine)-N-phenylamine)-triphenylamine (briefly: TNATA, pinfeed material).

1. A method for microstructuring by means of locally selectivesublimation, where patterns or images of organic electroluminescentcomponents are produced by applying a low-molecular emissions materialon a support by means of sublimation to the areas of a substrate whichcorrespond to a pattern or image to be produced, characterized in thatfirst a film support (1) made from a temperature resistant material iscompletely coated with the emissions material, the coated support (1)and the substrate (3) are then placed closely adjacent and parallel toeach other in a vacuum chamber (4), where the side of the support (1)that is coated with the emissions material faces the substrate (3), andon the side of the support (1) that is not coated, the areascorresponding to the pattern or image to be produced on the substrate(3) are then briefly and locally heated to a temperature that issufficient for the sublimation of the emissions material.
 2. A method asclaimed in claim 1, characterized in that a polyimide film is used forthe support (1).
 3. A method as claimed in claim 1 or 2, characterizedin that the support (1) is coated with two or more consecutivelow-molecular layers in a way so that the different materials of thelayers are not intermixed, while they form a mixed layer on thesubstrate (3) after the sublimation step.
 4. A method as claimed in oneof claims 1 to 3, characterized in that a structured electrical heatingelement is used to heat the support (1) locally.
 5. A method as claimedin one of claims 1 to 3, characterized in that laser radiation or lampradiation in conjunction with the corresponding optics are used to heatthe support (1) locally.
 6. A method as claimed in claim 1,characterized in that the low-molecular material is composed ofmaterials which improve the transport or the injection of electricalcharge carriers.